Counter ion effect on phase behavior in adsorbed film of fluoroalkanol and cationic surfactant mixture

The surface tension of the 1H,1H-heptafluoro-1-butanol (FC4OH)–dodecyltrimethylammonium chloride (DTAC) mixed aqueous solution was measured as a function of the total molality of the mixture and the composition of DTAC at 298.15 K under atmospheric pressure.The phase diagram of adsorption (PDA) that gives the composition relation between the aqueous solution and adsorbed film was constructed. It was suggested that the subtle balance between the attractive surfactant cation-OH dipole interaction and the weak dispersion interaction between C–H and C–F chains is crucial for the phase behavior. The phase diagram of adsorbed film (PDAF) showing the composition relation between the different state of adsorbed films demonstrated the phase behavior is significantly dependent on the degree of counter ion binding. Moreover, the possible surface structures at the azeotropes are suggested.